Frasier uses the Latin phrase "non qualm postea," which translates to "never again."
When Simon comes up to the roof to finish off Niles' and Daphne's leftovers, the door to the stairwell shuts. The audience can assume that he won't be able to enter the stairwell until the night watchman comes to open it during his rounds.
The title is the last line of the nursery rhyme "Hey Diddle Diddle, the Cat and the Fiddle."
Image of a naked man on the kitchen fridge/freezer. Totally out of context as all characters that live there are straight.